This invention relates in general to straddle-type cranes and, in particular, to a straddle-type crane which is especially adapted for use in handling watercraft on land. More specifically, but without restriction to the particular use which is shown and described, this invention relates to a straddle-type mobile hoist, wherein all of the lifting mechanisms may be power adjustable to facilitate the lifting, lowering, and transporting of boats having various hull designs. The lifting mechanisms are all positioned aft of a transversely-extending cross beam which joins the two parallel sides of the straddle crane to facilitate positioning of the lifting mechanism for improved balancing of a load supported therein.
The mobile hoist hereinafter described in detail in especially suitable for use in lifting, lowering, and transporting watercraft and will be described with reference to its use as a sling-rigged boat hoist. However, the structure disclosed hereinafter, and the manner in which that structure functions, can be utilized in applications other than for lifting, lowering, and transporting boats. For convenience of illustration, however, the hoist will be described with reference to its use in such an application.
Straddle-type mobile hoists may be used in harbor facilities to remove boats from the water, place them in storage, or convey them to a repair facility, as well as to remove boats from storage and replace them in the water. To this end, such straddle hoists are sling-rigged, and carry the boat on slings which are supported from an upper portion of the parallel sides of the crane with the slings passing beneath the boat hull to support and cradle the hull therein.
When placing a boat into or removing a boat from the water, these hoists are moved into a position straddling a slip formed between facing edges of two wharves, or piers, spaced a predetermined distance apart. The load-supporting slings may then be raised or lowered relative to the crane structure for removing a boat from the water, or placing the boat into the water, respectively.
Heretofore, such straddle cranes have utilized a forward or fore sling positioned in front of the cross-beam support which connects the parallel-spaced, longitudinally-extending, upper support beams from which the slings are supported. The fore sling has been supported in front of the transversely-extending cross beam in a fixed position which precludes the forward sling from being moved fore or aft relative to the transversely-extending upper support beams. Consequently, with such fixedly positioned forward slings, it is more difficult from the crane operator to correctly position the boat hoist to accommodate seacraft having sharply pitched hulls.
Frequently, with such straddle cranes, the boat has to be loaded onto the slings in a reverse direction so that the rear sling can be moved relative to the upper support beams in order to accommodate the shape of the boat hull. However, while such positioning will permit a better grip on a sharply pitched boat hull, loading in such a manner can also result in an undesirable weight distribution of the boat relative to the straddle hoist.